Method of manufacturing a replica as well as a replica obtained by carrying out an uv light-initiated cationic polymerization

ABSTRACT

The invention relates to a method of manufacturing a replica, which method comprises the provision of a polymerizable resin composition between a front mold having a pre-shaped surface and a back mold having a pre-shaped surface, carrying out a curing treatment and removing the replica thus manufactured from the molds. The invention further relates to a replica obtained by carrying out a UV light-initiated cationic polymerization.

The invention relates to a method of manufacturing a replica, whichmethod comprises the provision of a polymerizable resin between a frontmold having a pre-shaped surface, and a back mold having a pre-shapedsurface, carrying out a curing treatment and removing the replica thusmanufactured from the molds, which replica comprises a solid body ontowhich the shape of the surface of the front mold and the shape of thesurface of the back mold have been reproduced. The invention alsorelates to a replica obtained by carrying out a UV light-initiatedcationic polymerization.

Such a method is known per se from U.S. Pat. No. 4,890,905, filed in thename of the current applicant. The replication process employs a mold ora matrix having an accurately defined surface which is the negative ofthe desired optical profile of the replica. In the exact determinationof the definition of the surface of the mold or matrix, the shrinkage ofthe synthetic resin of the replica must be taken into account. Aquantity of a liquid, curable synthetic resin composition is provided inthe mold. The mold, comprising a front part and a back part, is closed,as a result of which the synthetic resin spreads between the pre-shapedsurfaces of the mold parts. The synthetic resin mixture is cured and thereplica is formed. Subsequently the replica is removed from the mold.The free surface of the synthetic resin replica is the negative of thecorresponding surfaces of the mold parts. The advantage of thereplication process is that optical components, such as lenses having acomplicated refractive surface, for example an aspherical surface, canbe manufactured in a comparatively simple manner without subjecting asubstrate, e.g. glass, to complex polishing treatments for obtaining thedesired surface shape. A drawback of such a replication by means ofpolymerization is the occurrence of shrinkage. Particularly if the flowof the bondable resin composition is impeded by gelation or asubstantial increase in viscosity, further polymerization will lead tothe development of stresses or even to premature delamination. If theproduct is subsequently removed from the mold, as in the case of, inparticular, a replication process, only a partial relaxation of thestresses takes place, particularly if the product formed is composed ofa densely cross-linked polymeric network. Such a bonded polymericnetwork is desired, however, for the cohesion of the product formed.

Therefore, it is an object of the invention to provide a polymerizableresin composition which, if it is cured against a mold, exhibits aslittle relaxation as possible after it has been removed from the moldand hence represents, as accurately as possible, the shape of the mold.

Another object of the invention is to provide a method of manufacturinga replica, which method employs a polymerizable resin composition whichalso features a high reaction rate and a reaction that can be controlledby UV radiation.

Still another object of the invention is to provide a method ofmanufacturing a replica in which method the polymerizable resin issubstantially insensitive to oxygen during curing so that parts of theresin that are not fully enclosed by the mold are still curable inambient air, thereby avoiding the need of blanketing said mold with aninert gas.

Yet another object of the invention is to provide a method ofmanufacturing a replica, which method employs a polymerizable resincomposition, the final product of which corresponds to the currentlyapplicable quality requirements regarding transparency and hardness.

A still further object of the invention is to provide a method ofmanufacturing a replica, wherein a polymerizable resin composition isemployed whose viscosity is so low that it can be accurately dosed inthe replica process without any problems.

The method mentioned in the opening paragraph is characterized inaccordance with the invention in that the curing treatment is a UVlight-initiated cationic polymerization, the resin composition usedbeing a compound comprising at least two cationically polymerizablecyclic ether groups, which only shows signs of gelation when at least30% of the conversion that can be achieved in the mold under therelevant curing conditions has taken place.

By using such a bondable resin composition, the final product will besubstantially free of shrinkage stresses owing to the late gelation andcomparatively small shrinkage. According to the applicant, thecomparatively small degree of shrinkage can be attributed to the factthat the ring-opening process on which the current curing treatment isbased does not cause a significant change of the number of chemicalbonds, instead the number of bonds in the starting product and in thebonded product more or less correspond to each other, so that only asmall degree of shrinkage takes place. Conversely, in the known(meth)acrylate compounds, as known from the above-mentioned U.S. Pat.No. 4,890,905, an increase in the number of chemical bonds is broughtabout, which explains the higher degree of shrinkage. In addition, inthe compounds in accordance with the invention, gelation andvitrification do not occur until a high conversion percentage isreached, so that the development of stresses starts at a much laterstage. According to the current applicants, this surprising effect isbrought about by a surprisingly large degree of chain transfer, as aresult of which, at the beginning of the bonding reaction, predominantlycomparatively small molecules are formed which do not form a gel until ahigh conversion percentage is reached. If the method in accordance withthe invention is applied to replicate aspherical lenses of, for example,CD players, the application of the bondable composition in accordancewith the invention will cause the shape of the mold to correspondsubstantially exactly to the product finally formed, as a result ofwhich a much smaller shrinkage correction is necessary. As, in addition,after the product has been removed from the mold, less relaxation isnecessary, it is to be expected that the amount of spread in the shapeof the replicated lenses will be much smaller in the above-mentionedproduction process. The method in accordance with the invention canparticularly suitably be used to replicate relief structures requiringan accurate (sub-micron) shape reproduction.

Compounds which can suitably be used in the method in accordance withthe invention to manufacture a replica include a bondable resincomposition of the following general formula:

-   -   wherein:    -   Y=—O—, —SO₂—, —CH₂—, —C(CF₃)₂—, —C(CH₃)₂—, —C(═O)—, —O—C(═O)—,        —O—C(═O)—O—,    -   X=a halogen or CH₃,    -   R₁=—CH₂—, —C(CH₃)₂—,    -   R₂=—OCH₂CH₂—, —OCCH₃HCH₂—, —OCH₂CCH₃H—, —OCH₂CHOHCH₂—,    -   R₃=H, C_(n)H_(2n+1),    -   n=an integer≧1,    -   p=1-4,    -   m, a, b, c are each individual integers in the range from 0-4.

For the bondable resin composition use can also suitably be made of acompound selected from the group formed by 1,2,7,8-diepoxyoctane,3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate,bis(3,4-epoxycyclohexylmethyl)adipate,bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate andC₁₂-C₁₄-alkylglycidylether and the corresponding oxetane compoundsthereof. An oxetane compound which can particularly suitably be used is1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene.

Dependent upon the viscosity of the selected bondable resin composition,it may be preferred, in certain embodiments, that the bondable resincomposition additionally comprises a reactive diluent, which ispreferably selected from the group formed by butylglycidylether,heptylglycidylether, octylglycidylether, allylglycidylether,p-t-butylphenylglycidylether, phenylglycidylether, cresylglycidylether,diglycidylether of 1,4-butanediol, diglycidylether of neopentylglycol,diglycidylether of polypropeneglycol, vinylcyclohexanedioxide,diglycidylether of recorcinol, diglycidylether of polypropeneglycol anddiglycidylester of linoleic acid dimer and the corresponding oxetanecompounds thereof.

The invention further relates to a replica obtained by carrying out a UVlight-initiated cationic polymerization of a compound comprising atleast two cationically polymerizable cyclic ether groups, which compounddoes not exhibit gelation until at least 30% of the conversion that canbe achieved in the mold under the relevant curing conditions has takenplace, if necessary in the presence of a reactive diluent.

A suitable replica is any relief structure requiring an accurate(sub-micron) reproduction. A further example of a suitable replica is anoptical component, in particular an (a)spherical lens, a lens array, aprism, a grating or another relief structure for optical applications,or a combination thereof.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiment (s) described hereinafter.

COMPARATIVE EXAMPLE

An aspherical lens is manufactured by means of a commonly knownphotoreplication method by providing a reactive mixture comprising amonomer, a photoinitiator and, if necessary, a sensitizer into anaspherical mold and pressed such as to cause the liquid to spreadbetween the pre-shaped surface of a front mold and the pre-shapedsurface of a back mold without the inclusion of air bubbles.Subsequently, the reactive mixture is exposed to UV light passingthrough at least one of said front and back mold and originating from ahigh-pressure mercury lamp provided with filters transmitting only thespectral range from 320 to 390 nm. If necessary, the exposure processcan be carried out such that the UV light passes through both the frontmold and the back mold, provided both molds are embodied so as to betransparent. After the exposure process, the lens is removed from themolds and optically and mechanically examined.

The above-mentioned photoreplication method is carried out using areactive mixture comprising a solution of 4%2,2-dimethyloxy-1,2-diphenylethane-1-on in2,2-bis(4-(2-methacryloxyeth-1-oxy)phenyl)propane. This mixture isexposed at room temperature for 7 seconds at an intensity of 40 mW/cm²and subsequently removed, whereafter it is re-exposed at 10 mW/cm² for 1hour at room temperature and stabilized in the dark for 16 hours at 140°C. The lens thus obtained is optically and mechanically characterized.

During the polymerization process, the mixture exhibited approximately7% shrinkage. Using such a reactive mixture, the aspherical mold must becorrected in an iterative process in order to obtain a lens of thedesired shape.

EXAMPLE IN ACCORDANCE WITH THE INVENTION

The commonly known photoreplication method described in the comparativeexample hereinabove is used, except that the reactive mixture used is asolution of 4.75% diphenyliodoniumhexafluoroarsenate and 0.25%anthracene in 2,2-bis(4-(glycidyloxy)phenyl) propane. This mixture issubsequently exposed at room temperature for 7 seconds at an intensityof 100 mW/cm² and subsequently removed, whereafter it is re-exposed at10 mW/cm² for 1 hour at room temperature, and stabilized in the dark at110° C. for 8 hours. The lens thus obtained is optically andmechanically characterized.

During the polymerization process, the mixture exhibited approximately2.3% shrinkage. Using such a reactive mixture comprising a compoundincluding at least two cationically polymerizable cyclic ether groups,it is not, or hardly, necessary, unlike the reactive mixture used in thecomparative example, to correct the aspherical mold in order to obtain alens of the desired shape. This favorable result is attributed to thefact that after removal from the mold, hardly any relaxation occurs.This very small degree of relaxation, as compared to the reactivemixture used in the comparative example, can be attributed, according tothe current applicants, to a combination of reduced shrinkage andretarded gelation.

The equipment for manufacturing the lenses should preferably include aprovision for movement of at least one of the molds in the axialdirection during the curing process as disclosed in U.S. Pat. No.4,477,328 or a provision for replenishment of monomer during cure asdisclosed in U.S. Pat. No. 4,812,346.

1. A method of manufacturing a replica, which method comprises theprovision of a polymerizable resin composition between a front moldhaving a pre-shaped surface, and a back mold having a pre-shapedsurface, carrying out a curing treatment and removing the replica thusmanufactured from the molds, which replica comprises a solid body ontowhich the shape of the surface of the front mold and the shape of thesurface of the back mold have been reproduced, characterized in that thecuring treatment is a UV-light initiated cationic polymerization, theresin composition used being a compound comprising at least twocationically polymerizable cyclic ether groups, which only shows signsof gelation when at least 30% of the conversion that can be achieved inthe mold under the relevant curing conditions has taken place.
 2. Amethod as claimed in claim 1, characterized in that the resincomposition further comprises a reactive diluent.
 3. A method as claimedin claim 1, characterized in that the compound is represented by thefollowing general formula:

wherein: Y=—O—, —SO2-, —CH2-, —C(CF₃)2-, —C(CH₃)2-, —C(═O)—, —O—C(═O)—,—O—C(═O)—O—, X=a halogen or CH3, R1=—CH2-, —C(CH₃)2-, R2=—OCH2CH2-,—OCCH3HCH2-, —OCH2CCH3H—, —OCH2CHOHCH2-,

R₃=H, C_(n)H_(2n+1), n=an integer≧1, p=1-4, m, a, b, c are eachindividual integers in the range from 0-4.
 4. A method as claimed inclaim 1, characterized in that the compound is selected from the groupformed by 1,2,7,8-diepoxyoctane,3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate,bis(3,4-epoxycyclohexylmethyl)adipate,bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate andC₁₂-C₁₄-alkylglycidylether and the corresponding oxetane compoundsthereof, in particular1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene.
 5. A method asclaimed in claim 1, characterized in that for the reactive diluent useis made of a compound selected from the group formed bybutylglycidylether, heptylglycidylether, octylglycidylether,allylglycidylether, p-t-butylphenylglycidylether, phenylglycidylether,cresylglycidylether, diglycidylether of 1,4-butanediol, diglycidyletherof neopentylglycol, diglycidylether of polypropeneglycol,vinylcyclohexanedioxide, diglycidylether of recorcinol, diglycidyletherof polypropeneglycol and diglycidylester of linoleic acid dimer and thecorresponding oxetane compounds thereof.
 6. A replica obtained bycarrying out a UV light-initiated cationic polymerization of a compoundcomprising at least two cationically polymerizable cyclic ether groups,which compound only exhibits gelation when at least 30% of theconversion that can be achieved in the mold under the relevant curingconditions has taken place, if necessary in the presence of a reactivediluent.
 7. A replica as claimed in claim 6, characterized in that thisreplica comprises a relief structure on at least one side, which reliefstructure must meet high (sub-micron) requirements with a view to thenecessary accuracy of form.
 8. A replica as claimed in claim 6,characterized in that the replica obtained is an optical component.
 9. Areplica as claimed in claim 8, characterized in that the opticalcomponent obtained is an (a)spherical lens, a lens array, a prism, agrating or another relief structure for optical applications, or acombination thereof.
 10. A replica as claimed in claim 6, characterizedin that the compound is represented by the following general formula:

wherein: Y=O—, —SO₂—, —CH₂—, —C(CF₃)₂—, —C(CH₃)₂—, —C(═O)—, —O—C(═O)—,—O—C(═O)—O— X=a halogen or CH₃, R₁=—CH₂—, —C(CH₃)₂—, R₂═—OCH₂CH₂—,—OCCH₃HCH₂—, —OCH₂CCH₃H—, —OCH₂CHOHCH₂—,

R₃=H, C_(n)H_(2n+1), n=an integer≧1, p=1-4, m, a, b, c are eachindividual integers in the range from 0-4.
 11. A replica as claimed inclaim 6, characterized in that the compound is selected from the groupformed by 1,2,7,8-diepoxyoctane,3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate,bis(3,4-epoxycyclohexylmethyl)adipate,bis(3,4-epoxy-6-methylcyclohexyl-methyl)adipate andC₁₂-C₁₄-alkylglycidylether and the corresponding oxetane compoundsthereof, in particular1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene.
 12. A replica asclaimed in claim 6, characterized in that for the reactive diluent useis made of a compound selected from the group formed bybutylglycidylether, heptylglycidylether, octylglycidylether,allylglycidylether, p-t-butylphenylglycidylether, phenylglycidylether,cresylglycidylether, diglycidylether of 1,4-butanediol, diglycidyletherof neopentylglycol, diglycidylether of polypropeneglycol,vinylcyclohexanedioxide, diglycidylether of recorcinol, diglycidyletherof polypropeneglycol and diglycidylester of linoleic acid dimer and thecorresponding oxetane compounds thereof.